FAIRBANKS, Alaska  They're a marvel of nature, birds that survive in a climate as hot as the Mojave Desert yet adapt quite comfortably in the coldest region of America's coldest state. Ravens survive the brutal cold of Alaska's North Slope by caching food, scavenging scrap from oil fields, and apparently by telling time, showing up when humans are mostly likely to leave food unguarded.

They are also smart enough to figure out which humans working around the oil rigs and miles of pipelines are most likely to be threats, trapping them and strapping on transmitters or wing tags.

"They're savvy creatures, and sometimes for me it was a question of who's going to be studied today," said researcher Stacia Backensto. "Are they studying me or I studying them? Who's in charge of this situation?"

Backensto, a biology and wildlife doctoral student at the University of Alaska Fairbanks, is enrolled in the school's regional resilience and adaptation program, in which students use both natural and social science to research northern problems. In Backensto's case, instead of focusing just on the biology of ravens, she studies the birds' interaction with the oil field workers.

Some admire and protect the ravens. Some see them as pests.

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"Most people I talk to have a story about them," Backensto said. But "to understand their behavior and try to observe their behavior and not be a part of changing their behavior is very tricky. It's like hide and seek."

One year into her research program, Backensto is amazed by the jet-black birds.

The ravens' breeding cycle starts sometime in late March, long before the snow melts on the North Slope, the vast treeless plain north of the Brooks Range that produces nearly 20 percent of America's domestic oil.

"It's still 30 below and females are laying and incubating eggs," Backensto said.

Ravens have nothing natural to hunt at that time of year and probably rely on food they've cached, she said. Structures in the oil field give them an opportunity to store food off the ground and away from four-legged competition, the arctic fox.

As the snow melts, ravens waddle along the tundra hunting lemmings. When migratory birds show up, the ravens become predators, stealing off with eggs or chicks in their beaks.

"It's brilliant timing for them, in that they have really large babies to feed and then a really nutritional resource available," Backensto said.

When prey is scarce, ravens compensate with other skills, such as telling time.

At one oil production unit, ravens would meet a cargo plane.

"They won't be out there all day, and then five minutes before the plane is scheduled to land, the ravens come in and they're by the runway and they wait," Backensto said. "What happens is they unload crates of food off of the plane and the ravens immediately descend upon these crates of food and start ripping open the packaging to get at the food."

Despite oil companies' best efforts to keep food from wild animals, ravens show up for crew shift changes, when many people are walking outside and there's a greater potential for food to be dropped. At Kuparuk, they seek out waste disposal trucks.

"The ravens follow the pickup trucks that go collect food waste. That's also like clockwork," she said. "They do it at a certain time of day and a certain time of night and they know which pickups to follow."

A Christmas bird count started in 1987 at the Prudhoe Bay landfill was the first indication that raven numbers were increasing. Backensto found little baseline information on the presence of ravens on the North Slope before oil drilling and began to suspect that raven numbers, like some other predators, were inflated around areas of high human activity.

"The main motivation for this research is that there are predators on the North Slope that for all purposes can be called subsidized predators," she said.

In addition to ravens, that includes grizzly bears, arctic fox and glaucous gulls -- scavenging species that can benefit from human food or structures.

Except for a few river bluffs, the North Slope lacks natural structures at least 23 feet high that ravens prefer for nesting. That may have limited their range in the far north until oil companies erected pipe and buildings.

"They can utilize these things to benefit their population," Backensto said. "They've got a higher food base, so right then their survival is up, their ability to reproduce and put out more offspring goes up."

More ravens could mean more predation on the tundra's summer visitors, migratory birds that fly north for breeding. That could someday mean measures to limit the raven population, Backensto said.

The same cleverness that allows ravens to thrive makes studying them a challenge.

"They're very wary of new things in their environment. If it's new, it has the potential to be dangerous," Backensto said.

It took her almost six weeks to trap a breeding raven using a leghold trap with a weak spring that would latch on without breaking legs. Using a drill-site operator's truck, Backensto finally buried the trap under snow in the truck bed. The "bait" was a brown paper lunch bag.

"This is what's familiar to them in their world," she said.

The birds mostly ignore oil field workers but can pick out Backensto's facial features and recognize her as the enemy despite borrowed coveralls and hard hat.

"There was one that was a very aggressive raven in Kuparuk," Backensto said. "The male -- and we didn't even trap the male, we trapped his mate, and put a radio transmitter on her -- chased us off the pad for a mile."